Mineral liberation through confined particle bed breakage

Fandrich, Rolf Gerald. (1998). Mineral liberation through confined particle bed breakage PhD Thesis, School of Engineering, The University of Queensland.

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Author Fandrich, Rolf Gerald.
Thesis Title Mineral liberation through confined particle bed breakage
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 1998
Thesis type PhD Thesis
Supervisor Dr. David Sutherland
Dr. Jim Boland
Total pages 321
Language eng
Subjects 09 Engineering
Formatted abstract
      The advent of High Pressure Grinding Rolls (HPGR) technology has focused attention on the mode of comminution known as confined particle bed breakage. The energy saving potential of HPGR mills has been proven, but the reported enhanced mineral liberation qualities have yet to be fully investigated or understood. The advent of reliable measurements of mineral liberation using image analysis now makes it possible to generate data that enables us to examine the liberation performance of confined particle bed breakage and subsequently model that performance. The hypothesis to be tested in this work is that the mineral liberation behaviour of a binary ore undergoing confined particle bed breakage can be modelled through an understanding of the breakage mechanisms taking place.

      A liberation modelling procedure based on the population balance approach is used to characterise the liberation performance of the confined particle bed breakage of a binary ore. The focus of this approach is the experimental determination of the bivariate breakage function that gives the transfer coefficients describing the movement of progeny particles in grade - size space from a parent particle of known grade and size. This bivariate breakage function can be characterised by a liberation and a comminution component.

      The experimental program undertaken to determine the bivariate breakage function involved the confined particle bed breakage of five narrow grade fractions of one narrow size fraction at three specific energy levels. Three manufactured grade distributions consisting of various proportions of six different narrow grade fractions were also broken for later validation of the liberation model. A grade dependent breakage model constituting the comminution component of the bivariate breakage function was developed from the size analysis of all progeny particles.

      Areal liberation analysis using QEM*SEM was performed on all progeny size fractions. The measured areal liberation spectra were corrected for stereological error using the Gay allocation method to obtain the volumetric liberation distributions. The measured liberation distributions at each progeny size constituted the conditional-on-size bivariate breakage function for that narrow grade fraction of parent particles. The first moment of these distributions defined the average grade of the distributions. Average grade was found to vary considerably with progeny size, being generally greater in the larger progeny size fractions and steadily decreased with progeny particle size. The iron oxide phase of the binary ore broke the silicate phase preferentially into finer size fractions. A measure of the slope of this decrease in average grade with progeny size was defined by the preferential breakage coefficient and was the basis for successfully modelling the internal structure of the conditional bivariate breakage function and the preferential breakage characterised by it.

      The bivariate breakage function used in the population balance equation was generated by an energy dependent liberation component and a grade dependent comminution component. The two are linked by a mathematical mechanism that enforced the law of phase conservation. The characterisation of the conditional-on-size bivariate breakage function for a particle also contained information regarding the phase content of the particles surrounding it, and hence actually breaking it. This information was necessary to successfully model preferential breakage using the population balance approach.

      The preferential breakage measured and quantified in this work is indicative of confined particle bed liberation. Theoretical considerations and analysis of the liberation mechanisms within confined particle beds support this conclusion. Another form of selective liberation, that of phase boundary fracture, was also investigated and quantified but did not contribute to the liberation modelling.
Keyword Ore-dressing -- Mathematical models.
Crushing machinery.

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
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Created: Tue, 28 Sep 2010, 10:50:50 EST by Muhammad Noman Ali on behalf of Social Sciences and Humanities Library Service